Black combs is frostbite. You need more ventilation in your coop. I personally don't heat my coop and yes, the rooster gets some frostbite but we've had three nights -20F already. At those temps the larger combs will get a touch of frozen. With heat lamps your raising the humidity and allowing frostbite to occur at any temp below freezing. If your bedding is damp then change it and get more ventilation in the coop. I'm not a proponent of heating but if you choose to know your birds wont go outside much and are in fact more susceptible to excessive moisture-frostbite.

You might want to try bag balm in the place of vasoline. It seems to absorb into the skin better.bag balm can be found at most feed stores and was first made for the sore utters of cows.its great stuff and I think it's better than vasoline.it comes in a green jar.hope this helps.